Isolation of D9-THC-a from hemp and analytical aspects concerning the determination of D9-THC in cannabis products,
by Dussy, Hamberg, Luginbiihl, Schwerzmann, and Briellmann,
from Institute of Legal Medicine
as published in Forensic Science International on line18-Aug-2004
Wow, lookee what Dr Fischedick shared with me, after being kind enough to listen to my enigma. Still working on the puzzlement, but getting closer and had some major insights reading this study done in Switzerland by the Institute of Legal Medicine.
Take a look at their extraction method at 2.2 and column chromatography purification procedure at 2.3 for lots of new ideas, and decarboxylation optimization results at 3.3, which with the Figure 8 graph, puts a whole new slant on thangs.
Hee, hee, hee, enjoy and hats off to Dr Fischedick for the link! Copies of the study at:
http://www.sciencedirect.com/science/article/pii/S0379073804003408
Here are some high points paraphrased:
2.2. Extracting D9-THCA-a
The extraction was done per Lehmann and Brenneisen procedure.
100 g of 5% D9 THC content was pulverized and extracted using 500 mL petroleum ether, which hac been acidified with 0.5 mL acetic acid (0.5 mL CH3COOH in 500 mL PE).
The filtrate was re-extracted three times, using 400 mL 2% aqueous NaOH and Na2SO3 (2% each). The 1200 mL of solution was acidified using 500 mL of 5% glacial sulfuric acid, to reach a pH of 3, followed by an immediate extraction using three times 400 mL TBME.
The extracts were dried using Na2SO4, followed by filtration and concentration using a rotary evaporator at 25–30 8C. After overnight drying under vacuum, it yielded 1.71 grams of a brown amorphous solid.
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2.3. Purifying the crude extract using column chromatography.
They chromatographed a hundred and seventy-seven milligrams crude extract, using a 30 mm _ 400 mm column, packed with 0.063–0.2 mm 100 g silica 60 ().
An elution solvent was used consisting of 650 mL hexane, 215 mL toluene, 135 mL Acetone and 20 drops of acetic acid. It was passed through the column at 1.5 mL/min.
D9-THCA-A began eluting at 280 mL. They collected the fractions from 290 mL until 510 mL
and concentrated them in a 25–30 8C rotary evaporator at . After overnight drying under vacuum conditions it yielded 99 mg pale yellow amorphous solid.
The sample tested 96% pure D9-THCA-A by 1H-NMR, with the principle impurity being CBN.
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Fig. 8 shows that 150C is about the optimum THC-a decarboxylation temperature, with a yield of around 70%, the balance oxidizing into cannabinol.
Figure 8
Given that the sum of D9-THCA-A, D9-THC and cannabinol doesn’t total 100%, the assumption is made that other polymeric material is also formed.
A change in temperature, requires an attendant adjustment in exposure time to maximize yield.
There is no significant temperature dependence observed between 140 and 160 C, so an exact temperature setting is not critical within that range.
The significance that I see in graph Fig 8, is that the previous assumption has been that at 70% decarboxylation that the rate of conversion of the remaining 30% THC-a tp THC, was at a lower rate that the conversion of THC to CBN, but this graph shows THC-a to THC is maxed out at 70% and the decline in total THC is due to conversion to CBN.